Mobile ECG sensor apparatus

ABSTRACT

Disclosed systems include mobile ECG sensors, systems and methods. Some embodiments provide ECG sensors in a credit card form factor that allows a user to contact two electrically isolated electrodes to measure heart electrical signals for a Lead I ECG.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 15/721,038, filed Sep. 29, 2017, now PublicationUS-2018-0020939, which is a continuation of U.S. patent application Ser.No. 15/140,072, filed Apr. 27, 2016, now U.S. Pat. No. 9,833,158, whichis a continuation of U.S. patent application Ser. No. 14/254,310, filedApr. 16, 2014, now U.S. Pat. No. 9,351,654, which is acontinuation-in-part of U.S. patent application Ser. No. 13/108,738,filed May 16, 2011, which is a continuation-in-part of U.S. patentapplication Ser. No. 12/796,188, filed Jun. 8, 2010, now U.S. Pat. No.8,509,882

This application is also a continuation-in-part of U.S. patentapplication Ser. No. 15/486,777, filed Apr. 13, 2017, now PublicationUS-2017-0215755, which is a continuation of U.S. patent application Ser.No. 13/964,490, filed Aug. 12, 2013, now U.S. Pat. No. 9,649,042, whichis a divisional of U.S. patent application Ser. No. 12/796,188, filedJun. 8, 2011, now U.S. Pat. No. 8,509,882, each of which is incorporatedherein by reference in its entirety.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

BACKGROUND 1. Field of Invention

The presently claimed and disclosed inventive concept(s) relatesgenerally to personal physiology monitoring devices and methods and,more particularly, but not by way of limitation, to devices, systems andsoftware for providing ECG, heart rate and cardiac arrhythmia monitoringutilizing a computing device such as a smartphone.

2. Background of the Invention

The prior art includes numerous systems wherein ECG data or the like ismonitored and/or transmitted from a patient to a particular doctor'soffice or health service center. For example, U.S. Pat. No. 5,735,285discloses use of a handheld device that converts a patient's ECG signalinto a frequency modulated audio signal that may then be analyzed byaudio inputting via a telephone system to a selected hand-held computerdevice or to a designated doctor's office. Similarly, U.S. Pat. No.6,264,614 discloses a heart monitor, which is manipulated by the patientto sense a biological function such as a heart beat, and outputs anaudible signal to a computer microphone. The computer processes theaudible signal and sends resulting data signals over a network orInternet. U.S. Pat. No. 6,685,633 discloses a heart monitor that apatient can hold against his or her chest. The device outputs an audiblesignal responsive to the function or condition, such as the beating ofthe heart to a microphone connected to a computer. Each of these audiotransmissions is limited to transmission of audible sound. In otherwords, frequency modulated sound transmission at carrier frequenciesabove that heard by humans, i.e. above 17 kHz, was not contemplated.

U.S. Pat. App. Publication No. 2004/0220487 discloses a system with ECGelectrodes which sense ECG electrical signals which are combined andamplitude modulated. The composite signal is transmitted via wire orwirelessly to the sound port in a computing device. A digital band passfilter having a pass band from 19 kHz to 21 kHz is considered; however,there is no consideration of demodulation means at this frequency rangeusing commercially available computing devices. Additionally, the use ofsound waves to effect transmission is not contemplated.

U.S. Pat. App. Publication No. 2010/0113950 discloses an electronicdevice having a heart sensor including several leads for detecting auser's cardiac signals. The leads are coupled to interior surfaces ofthe electronic device housing to hide the sensor from view. Using thedetected signals, the electronic device can then identify orauthenticate the user.

U.S. Pat. No. 6,820,057 discloses a system to acquire, record, andtransmit ECG data wherein the ECG signals are encoded in a frequencymodulated audio tone having a carrier tone in the audio range. However,there is no real consideration of carrier frequencies above about 3 kHz,no consideration of carrier frequencies above the audible, and noconsideration of demodulation methods at higher carrier frequencies.

Limitations of the prior art utilizing transtelephonic and audibleacoustic signals include a signal to noise ratio that is diminished bytalking or any other noisy activity in the vicinity, thus potentiallyjeopardizing the integrity of the heart monitoring data signals.Additionally, the audible signals can be heard by anyone in the vicinityof the computer and heart monitor, which can be bothersome to the useras well as to others in the vicinity. Other applications fail to providea reliable, inexpensive personal monitoring device that is readilycompatible with existing computing devices such as smartphones. It wouldbe advantageous if these issues were addressed in a personal monitoringdevice transmitting real time physiological data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial representation of the human range and thresholdsof hearing from http://en.labs.wikimedia.org/wiki/Acoustics.

FIG. 2 is a pictorial representation of hearing loss with age fromwww.neuroreille.com/promenade/english/audiometry/audiometry.htm.

FIG. 3 is an audiogram illustrating the intensity and frequency ofcommon sounds from www.hearinglossky.org/hlasurvival1.html.

FIG. 4 is a schematic representation of an embodiment of a personalmonitoring device transmitting to a computing device.

FIG. 5 is a schematic representation of another embodiment of a personalmonitoring device of the present invention.

FIG. 6 is an example of graphical ECG representation.

FIG. 7A is a spectrogram of the noise in a quiet office environment.

FIG. 7B is a spectrogram of a modulated ultrasonic signal from an ECGmonitoring device embodied in the present invention.

FIG. 8A is a schematic representation of an embodiment of a personalmonitoring device of the present invention having a tubular shape.

FIG. 8B is a schematic representation of another embodiment of apersonal monitoring device of the present invention usable as asmartphone protective case.

FIG. 8C is a schematic representation of an embodiment of a personalmonitoring device of the present invention usable as a pad.

FIG. 9A is a perspective view of one embodiment of the present inventionwith a credit card form factor.

FIG. 9B depicts the underside of the upper layer of the embodiment ofthe present invention shown in FIG. 9A.

FIG. 9C depicts the topside of the upper layer of the embodiment of thepresent invention shown in FIG. 9A.

FIG. 10 is a perspective view of a personal monitoring device inaccordance with one embodiment of the present invention.

FIG. 11 is a schematic representation of an embodiment of an ECG deviceof the present invention included positioned within a chest strap.

FIG. 12 is a schematic representation of a computer-readable storagemedium embodiment of the present invention.

FIG. 13 is a schematic representation of an embodiment of the presentinvention.

FIG. 14 is an example representation of a frequency spectrum afterbandpass filtering.

FIG. 15 is an example representation of a frequency spectrum afterunder-sampling at half the original sampling rate.

FIG. 16 illustrates a working example of a system for receiving anddemodulating an ultrasonic FM ECG sound signal.

DETAILED DESCRIPTION

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not limited in its applicationto the details of construction, experiments, exemplary data, and/or thearrangement of the components set forth in the following description.The invention is capable of other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that theterminology employed herein is for purpose of description and should notbe regarded as limiting.

In the following detailed description of embodiments of the disclosure,numerous specific details are set forth in order to provide a morethorough understanding of the disclosure. However, it will be apparentto one of ordinary skill in the art that the concepts within thedisclosure can be practiced without these specific details. In otherinstances, well-known features have not been described in detail toavoid unnecessarily complicating the description.

The human hearing range is often referred to as 20 Hz to 20 kHz. Amaximum aural range in children, under ideal laboratory conditions, isactually as low as 12 Hz and as high as 20 kHz. However, as shown inFIG. 1, the threshold frequency, i.e. the minimum intensity detectable,rises rapidly to the pain threshold between 10 kHz to 20 kHz. Thus,sounds above about 16 kHz must be fairly intense to be heard. Almostimmediately from birth, the threshold sound level for these higherfrequencies increases. As shown in FIG. 2, an average 20 year old haslost about 10 dB in the 8 kHz range, while at age 90, the average personhas lost over 100 dB at this frequency.

An example product using very high frequency sound is the Mosquitoalarm, a controversial device emitting an intentionally annoying 17.4kHz alarm and used to discourage younger people from loitering. Due toadult hearing loss at this frequency, it is typically heard only bypeople less than 25 years of age. Similarly, students make use of theadult hearing loss by using “mosquito” ringtones in the 15-17 kHz ontheir cell phones during school. The students can hear the “mosquito”ringtones while their adult teachers cannot. The term “ultrasonic”typically means above the range perceived by humans. However, asdemonstrated, the upper limit of hearing frequency varies withindividuals and with age generally. Because of the differences in thisupper limit, the term “ultrasonic” is defined herein and in theappending claims to refer to “sound frequencies of 17 kHz or greater.”

Interestingly, however, there is very little ambient sound or noiseabove about 10 kHz. Referring to FIG. 3, most everyday sounds occur atfrequencies below about 4 kHz. Thus, use of signals in the ultrasonicrange is not only silent to those around, but also provides a verydesirable signal to noise ratio (SNR).

Acoustic engineers safely assume that any frequency above about 20 kHzwill have no effect on the perceived sound and they filter everythingabove this range. Sounds below 20 kHz but still in the ultrasonic rangeare of little concern, and standard sampling procedures have beenestablished accordingly. It is generally understood that sampling ananalog signal, whether a radio signal or audible sound signal, requiresa sampling frequency f_(s) such that f_(s)/2>f, wherein f is thesinusoid frequency. For this reason, sound systems are designed tosample the sound at the now standard sample rate of 44.1 kHz, setsomewhat higher than the calculated Nyquist-Shannon sampling rate of 40kHz for a 20 kHz sound upper limit. Actual demodulation of an FM narrowband signal in the ultrasonic range, using existing demodulationprocedures, computers, telephones, cell phones, stereo sound systems,etc., would result in very poor reproduction of the original signal.This is unfortunate because, as discussed above, a carrier signal in theultrasonic range would also have a very low signal to noise ratio due tothe fact that there is very little natural “noise” at these higherfrequencies.

The inventive concept(s) disclosed herein is directed to a personalmonitoring device, methods and systems for measuring physiologicalsignals and transmitting those measurements wirelessly and soundlesslyusing frequency modulated ultrasonic signals having a much improvedsignal to noise ratio compared to traditional transtelephonic methods.Also provided are methods and algorithms to receive and demodulate theultrasonic signals with excellent accuracy using existing computer andsmart phone technology.

The presently claimed and disclosed inventive concepts provide apersonal monitoring device 10, embodiments of which are shownschematically in FIG. 4 and FIG. 5. The acquisition electronics 11 ofthe monitoring device 10 includes a sensor assembly 12 configured tosense physiological signals upon contact with a user's skin. The sensorassembly 12 produces electrical signals representing the sensedphysiological signals, which input to a converter assembly 14,integrated with the sensor assembly 12. Converter assembly 14 convertsthe electrical signals generated by the sensor assembly 12 to afrequency modulated ultrasonic signal which is output by ultrasonictransmitter 24. In one embodiment, the frequency modulated ultrasonicsignal has a carrier frequency in the range of from about 18 kHz toabout 24 kHz. In another embodiment, the frequency modulated ultrasonicsignal has a carrier frequency in the range of from about 20 kHz toabout 24 kHz.

The sensor assembly 12 can include any suitable sensor operative todetect a physiological signal that a user desires to monitor.Nonlimiting examples of such physiological signals include, but are notlimited to, respiration, heart beat, heart rate, electrocardiogram(ECG), electromyogram (EMG), electrooculogram (EOG), pulse oximetry,photoplethysmogram (PPG) and electroencephalogram (EEG).

A respiration detector can be a conventional microphone assistedstethoscope 12′. Heart beat and heart rate can be detected as well usinga conventional microphone assisted stethoscope 12′, or by using anelectrode assembly 18 to sense electrical signals generated by the heartover time. Such electrodes 18 can also be used to detect the electricalactivity of the heart over time for electrocardiography (ECG). An ECG isa measurement of the small electrical changes on the skin generated whenthe heart muscle depolarizes during each heart beat. The output from apair of electrodes 18 is known as a lead 20. Small rises and falls inthe voltage between two electrodes placed on either side of the heartcan be processed to produce a graphical ECG representation 22 such asthe example ECG shown in FIG. 6.

Electromyography (EMG) detects the electrical potential generated bymuscle cells when the cells are electrically or neurologicallyactivated. The signals can be analyzed to detect medical abnormalities.Electrooculography (EOG) is a technique for measuring the restingpotential of the retina. Usually, pairs of electrodes 18 are placedeither above and below the eye, or to the left and right of the eye, anda potential difference measurement is a measure for the eye position.

The oxygenation of a person's hemoglobin can be monitored indirectly ina noninvasive manner using a pulse oximetry sensor, rather thanmeasuring directly from a blood sample. The sensor is placed on a thinpart of the person's body, such as a fingertip or earlobe, and a lightcontaining both red and infrared wavelengths is passed from one side tothe other. The change in absorbance of each of the two wavelengths ismeasured and the difference used to estimate oxygen saturation of aperson's blood and changes in blood volume in the skin. Aphotoplethysmogram (PPG) can then be obtained using the pulse oximetersensor or with an optical sensor using a single light source. The PPGcan be used to measure blood flow and heart rate. Anelectroencephelogram (EEG) can be monitored using electrodes attached tothe scalp and measures voltages generated by brain activity.

The converter assembly 14 converts the electrical signals generated bythe sensor assembly 12 to a frequency modulated ultrasonic signal thatcan be received by a computing device 16. In the embodiment shown inFIG. 5, the converter assembly 14 includes a converter 23 and anultrasonic transmitter 24 for outputting frequency modulated ultrasonicsignals having a carrier frequency in a range of from, for example,about 18 kHz to about 24 kHz. Nonlimiting examples of suitableultrasonic transmitters 24 include, but are not limited to, miniaturespeakers, piezoelectric buzzers, and the like. The ultrasonic signalscan be received by, for example, a microphone 25 in a computing device16 such as a smartphone 30, personal digital assistant (PDA), tabletpersonal computer, pocket personal computer, notebook computer, desktopcomputer, server computer, and the like.

Prior art devices have used frequency modulated physiological signals tocommunicate between acquisition hardware and a computing device. Thesignals have a carrier frequency within the audible range such as thetraditional 1.9 kHz FM frequency used to transmit ECG signals. However,it has been discovered that by using ultrasonic frequencies as thecarrier, such as frequencies in the range of from about 18 kHz to about24 kHz, and even 20 kHz to 24 kHz, the acoustic communication betweenthe acquisition electronics 11 of the personal monitoring device 10, anda computing device 16 such as a smartphone, is virtually silent and farmore noise-immune than the traditional 1.9 kHz FM ECG frequency. Infact, measurements of the audio signal power in the ultrasonic rangedetermined that carrier frequencies of 17 kHz and higher providecommunication that is immune to ambient and voice “noise” contamination.By using an ultrasonic carrier frequency, in even the “noisiest”environment, we create both a noise-free and a silent communicationbetween the acquisition electronics 11 and the computing device 16 suchas a smartphone 30, notebook computer, or the like.

For example, FIG. 7A shows a spectrogram of the sound in a quiet officeenvironment. As can be seen, the ambient noise is about 35 db at 2 kHz.FIG. 7B shows a spectrogram of the ultrasonic modulated ECG signal inthe same quiet office environment. It should be noted that the ambientnoise at 19 kHz is only 20 db (the slight upturn is artifact) giving atleast a 15 db advantage for a 19 kHz ultrasonic signal compared to astandard 2 kHz signal. This is a significant improvement on the signalto noise ratio (SNR) which improves even more in noisy environments suchas the street, shopping mall or a noisy home. Synergistically, thevolume of the signal can be further increased at the ultrasonicfrequencies, without concern for “listeners” present, because theycannot hear it.

In one embodiment, the personal monitoring device 10 is an ECG device10′ and includes an electrode assembly 18 configured to senseheart-related signals upon contact with a user's skin, and to convertthe sensed heart-related signals to an ECG electric signal. As discussedin detail hereinafter, the ECG device 10′ transmits an ultrasonicfrequency modulated ECG signal to a computing device 16 such as, forexample, a smartphone 30. Software running on the computer 16 orsmartphone 30 digitizes and processes the audio in real-time, where thefrequency modulated ECG signal is demodulated. The ECG can be furtherprocessed using algorithms to calculate heart rate and identifyarrhythmias. The ECG, heart rate, and rhythm information can bedisplayed on the computer 16 or smartphone 30, stored locally for laterretrieval, and/or transmitted in real-time to a web server 52 via a2G/3G/4G, WiFi or other Internet connection. In addition to the displayand local processing of the ECG data, the computer 16 or smartphone 30can transmit, in real-time, the ECG, heart rate and rhythm data via asecure web connection for viewing, storage and further analysis via aweb browser interface (using the 2G/3G/4G or WiFi connectivity of, forexample, the smartphone 30). Server software provides for storage,further processing, real-time or retrospective display and formulationof a PDF ECG rhythm strip document and/or other reports and formats forprinting remotely or locally.

In another embodiment, the converter assembly 14 of ECG device 10′ isintegrated with, and electrically connected to the electrode assembly 18and is configured to convert the electric ECG signal generated byelectrode assembly 18 to a frequency modulated ECG ultrasonic signalhaving a carrier frequency in the range of from about 18 kHz to about 24kHz. It is sometimes desirable to utilize a carrier frequency in the 20kHz to 24 kHz range. The ultrasonic range creates both a lower noise anda silent communication between the acquisition electronics 11 and thecomputing device 16 such as the smartphone 30, notebook, and the like.

The ECG device 10′ can be configured in any way consistent with itsfunction, i.e., it should include electrodes available to make contactwith a user's skin on the hands, chest or other parts of the body, forobtaining the user's ECG, and means for transmitting the ECG usingultrasound to a receiving device. For example, a hand held ECG device10′ can be shaped like a credit card as in FIG. 5 with two electrodes onthe bottom surface, or the ECG device 10′ can be shaped like a flashlight or pen as in FIG. 8A having one electrode 18 on the cylindricalsurface 57 touching a holder's hand, and the other electrode 18′ is onan end 59 contacting the chest, hand or other body part when in use.

In another configuration, the ECG device 10′ is usable as a smartphoneprotective case 60 as shown in FIG. 8B. One example configurationutilizes a “slip-on” protective case 60 for an iPhone® or othersmartphone 30, the protective case 60 including an integrated ECGelectrode assembly 18 and acquisition electronics 11 (2, 3 or 4electrodes for generating a single lead of ECG data). The ECG electrodesare located on the side 62 of the case 60 opposite of the display screen58. The smartphone 30, in its ECG-adapted protective case 60, can beheld in both hands (generating a lead one, Left Arm minus Right Arm) orcan be placed on a person's chest to generate a modified chest lead. TheECG is measured by the acquisition electronics 11 and converted into afrequency modulated ultrasonic signal. Nonlimiting example of suitablecarrier or center frequencies include from about 18 kHz to about 24 kHz,or in some embodiments from about 20 kHz to 24 kHz. The frequencymodulated ultrasonic signal is output by a miniature speaker 64 or apiezoelectric buzzer 66.

FIG. 9A shows another embodiment of a credit card like monitoring device100 (“credit card sensor”), similar to that depicted as 10′ in FIG. 5A,for remote or mobile acquisition of ECG data. Some embodiments may havea similar form as a financial bank or credit card, which may have athickness of approximately 0.75 mm, and may be flexible and made of aplastic or polymer, such as polyvinyl chloride acetate (PVCA). Someembodiments of the credit card sensor have a thickness between 0.65 mmto 0.85 mm, and some between 0.70-0.78 mm. Some embodiments of thecredit card sensor may have a range of bending stiffness, and some maymeet the standards outlined by ISO 7810 ID-1 format. Embodiments of thecredit card like sensor may have a bending stiffness or flexibilitypermitting a user to place it in a purse or wallet in a similar mannerto how a normal credit card is stored and carried.

Referring to FIG. 9A, a perspective view of an embodiment of credit cardsensor 100 is depicted. Credit card sensor 100 has a sandwich structurewith upper layer 102 and lower layer 104, width a, length b andthickness c. FIG. 9B shows underside 103 of upper layer 102. Underside103 has flexible membrane electrodes 106, one on each side of creditcard sensor 100, converter 108 battery 109, piezo ultrasonic soundemitter 110, power button 112, and LED indicator 114. Battery 109 powersconverter 108, which may be a printed circuit board with firmwareinstalled thereon. FIG. 9C depicts topside 101 of upper layer 102.Topside 101 has exposed touch pads 105 that are in electrical contactwith flexible membrane electrodes 106.

As described herein, a user contacts touch pads 105 (e.g., left andright fingers) that sense an electric signal for a Lead I ECG. Converter108 converts the electrical signals generated from the touch pads 105 toa frequency modulated signal, for example an ultrasonic signal orBluetooth signal (further described below), that can be received by acomputing device 116. In the embodiment shown in FIGS. 9A-9C. Theconverter assembly includes a converter 108 and an ultrasonictransmitter 110 for outputting frequency modulated ultrasonic signalshaving a carrier frequency in a range of from, for example, about 18 kHzto about 24 kHz. The ultrasonic signals can be received by, for example,a microphone in computing device 116 such as a smartphone (as shown),personal digital assistant (PDA), tablet personal computer, pocketpersonal computer, notebook computer, desktop computer, server computer,smart watch or wearable, and the like. Computing device 116 has amicroprocessor/CPU (not shown) that may do one or more of the following:acquire, digitize, demodulate, process and then display ECG data inreal-time.

In an alternative embodiment, credit card sensor 100 may have a display(not shown) allowing near real time display of a user's ECG. In thisembodiment, for example, credit card sensor 100 may include a receiver(not shown), which may be included with converter 108, that receives theprocessed ECG signal from the computing device and displays it on adisplay (not shown) on the credit card sensor 100. Alternatively, creditcard sensor 100 may include a processor (not shown), which may beincluded with converter 108 having the ability to process and displaythe signals from touch pads 105 in a similar manner as the CPU ofcomputing device 116. In this embodiment, all connections may be hardwired or wireless. Credit card sensor 100 may include memory (notshown), which may be part of or separate from converter 108, or theprocessor may include firmware (not shown), where the memory or firmwaremay include instructions for causing the processor to process the sensedheart-signals (e.g., ECG signals etc.) from a user contacting the touchpads 105 and displaying the heart-signals on a display (not shown)located on an exterior surface of credit card sensor 100. Transmitter110 may be used to transmit the processed signal to a computing device,where a medical professional may view the recording. Alternatively,computing device, once in receipt of the data, may send the data to amedical professional using well know communications and data transfertechnologies.

In yet another embodiment, shown in FIGS. 10 (formerly 7 of '042) and 11(formerly 8 of '042), converter assembly 108 includes a wireless radiotransmitter 37 configured to convert and transmit the electrical signalsgenerated by the sensor assembly 12 using a headset profile (HSP) of theBluetooth® wireless communications standard is defined by the BluetoothSpecial Interest Group (SIG) and available at URL addresswww.bluetooth.org. The electrical signals generated by the sensorassembly 12 are converted and transmitted using a Bluetooth® transceiver34 and antenna 36 and communicated to the computing device 13,preferably a smartphone 30 or smart watch, according to instructionsprovided by a headset controller 38. Economy, as well as isolation andconvenience, are provided by using a commercially available headsetcontroller 38, Bluetooth® transceiver 34, and antenna 36, powered by aheadset battery 40, wherein the electronics are commercially configuredand mass-produced for communicating with computing devices 13 such assmartphones 30.

Computing device electronics 42 typically include a controller 44, aBluetooth® transceiver 46 and antenna 48 for receiving input from awireless Bluetooth® device. Most computing devices, and all smartphonesand most wearables, include a memory 56, a display screen 58, and atransceiver 50 for transmitting/receiving information signals to/from abase station or web server 52 via a cellular antenna 54, or WiFiconnection. Thus, the computing device electronics 42 can be used tostore information from the personal monitoring device 10 in memory 56,and/or transmit the information to the base station 52 or a specificcommunication address is wireless communication technology wellunderstood by those skilled in the art.

In yet another embodiment, shown schematically in FIG. 11, the ECGdevice 10′ is usable as a chest strap device 68 like a fitness heartrate monitor. The chest strap 69 with integrated ECG electrode assembly18 and acquisition electronics 11 “pod” generate the frequency modulatedultrasonic ECG signal and send it to a computing device 16 such as thesmartphone 30.

In any of the configurations, the computing device 16, such smartphone30, utilizes its built-in microphone 25 and CPU to acquire, digitize,demodulate, process and then display the ECG data, in real-time. Also,the computing device 16, smartphone 30 or smart watch can calculate areal-time heart rate measurement and determine a cardiac rhythmdiagnosis like atrial fibrillation. The computing device 16 orsmartphone 30 can utilize its 2G, 3G, 4G, Bluetooth® and WiFiconnectivity to transmit the ECG and other data to a secure web server52 for real-time distant display, storage and analysis. Also, the ECGdata can be stored locally on the smartphone 30 for later review ortransmission.

Software on the smartphone 30 can also combine data and signals fromother sensors built into the smartphone 30 such as a GPS andaccelerometer. Further processing of this data provides additionalinformation related to the user, such as speed, location, distance,steps, cadence, body position, fail detection and energy expenditure.The raw signals from the sensors and derived information can bedisplayed and stored locally on the smartphone 30, as well as beingtransmitted to the web server 52 over an internet connection. Softwareon the web server 52 provides a web browser interface for real-time orretrospective display of the signals and information received from thesmartphone 30, and also includes further analysis and reporting.

Referring now to FIG. 12, a computer-readable storage medium 56 stores aset of instructions 72, wherein the instructions 72 are capable of beingexecuted by one or more computing devices 16. Nonlimiting examples ofsuitable computing devices 16 include smartphones 30, personal digitalassistants (PDAs), tablet personal computers, pocket personal computers,notebook computers, desktop computers, and server computers. When theinstructions 72 are executed, the one or more computing devices 16 iscaused to digitize and demodulate a sensor input 74 such as anultrasonic frequency modulated ECG signal to produce real-timedemodulated digital ECG data. The instructions 72 can also cause thereal-time demodulated digital ECG data to display on a display screen 58of the computing device 16.

A common technique used for FM demodulation is based on zero crossingdetection where the time interval between zero crossings is used tocalculate the frequency and reconstruct the demodulated signal. In someapplications simply counting the number of audio samples between zerocrossings may provide sufficient accuracy for frequency estimation.Accuracy can be improved by interpolating between samples which providesa better estimate of the zero crossing point and subsequent frequencyestimation. FM demodulation based on zero crossing detection is simpleto implement and requires little computation compared with othertechniques such as those using FFT's (fast Fourier transforms), makingit particularly suitable for use in real-time applications on low powerportable computing devices.

However, if the FM narrow band signal is close to the Nyquist frequencyof the digitally sampled audio, the error in the zero crossing estimatesbecome large, as there are very few samples per cycle. This severelylimits the use of typical zero crossing demodulation techniques forultrasonic carrier frequencies. An embodiment of the present disclosureprovides a method to demodulate FM narrow band signals close to theNyquist frequency, while maintaining the simplicity and efficiency ofthe zero crossing technique, with accurate frequency estimation.

Referring now to FIG. 13, an ultrasonic FM signal representing ECGsignals is picked up by a microphone 25 in, for example, a mobile phone30 or other computing device 16, and converted to an analog signal. Theanalog signal is continuous in time and is converted to a flow ofdigital values in an analog-to-digital converter 80, demodulated in FMdemodulator 82 and shown on a display 58 of the smart phone 30 or othercomputing device 16, or retained in storage memory 56. Since a practicalanalog-to-digital converter 80, commonly referred to as an ADC, cannotmake an instantaneous conversion, the input value must necessarily beheld constant during the time that the converter performs a conversion.The rate at which the new digital values are sampled from the analogsignal is called the sampling rate or sampling frequency of the ADC.Mobile phones and other personal computing devices are typically limitedto recording audio at 44 kHz. Some smart phones such as ANDROID® andIPHONE® can sample at 48 kHz.

The digitized ultrasonic signal can then be bandpass filtered around theultrasonic carrier frequency of the FM signal to improve signal-to-noiseand reduce unwanted audio outside the passband. The filtered FM signal,as depicted in FIG. 14, is then “under-sampled” at half the samplingrate of the original audio. This results in aliasing of the FM signalthat shifts and inverts the frequency spectrum to a lower frequencyband. The result of the frequency spectrum being inverted by theunder-sampling operation, results in the demodulated output beinginverted as depicted in FIG. 15. The inversion is corrected by simplyconverting the final demodulated output.

With the FM signal at a lower frequency there are more audio samples percycle and demodulation processes, such as zero crossing estimates, aresignificantly more accurate. For example, the zero crossing detectoridentifies the zero crossings where the audio signal changes sign. Theaccuracy of the zero crossing point is further improved by linearlyinterpolating between samples either side of the zero crossing. Finally,the period between zero crossings is used to calculate an estimate ofthe frequency and reconstruct the demodulated signal. While theabove-described demodulation procedure utilizes a zero crossingestimate, it is understood that other demodulation procedures can beutilized and that the accuracy of other demodulation procedures willalso benefit from the under-sampling operation.

EXAMPLE

In one working example, illustrated in FIG. 16, a system used anultrasonic FM ECG signal transmitted from a portable ECG monitor to amicrophone 25 in a mobile phone 30 as well as a personal computer 16.This provided a low-cost wireless transmission solution that iscompatible with most mobile phones and computers that have a microphone,without requiring any additional hardware to receive the signal.

It is desirable that the FM signal is above 18 kHz, so that is inaudibleto most people, does not interfere with music or speech, and is alsoless prone to audio interference. It is also desirable for the FM signalto have a narrow bandwidth to further reduce its susceptibility to audiointerference. In this case the ECG monitor used an ultrasonic FM carrierof 19 kHz, modulated with an ECG at 200 Hz/mV and having a range of ±5mV. This resulted in an ultrasonic FM signal between 18 kHz and 20 kHz.

First, the audio FM signal was picked up by a microphone 25 anddigitized by the ADC 80 in the mobile phone 30 at 44 kHz. The audio wasthen bandpass filtered in filter 82 between 18 kHz and 20 kHz to removeaudio noise outside the pass band. In the next stage 84 the audio wasunder-sampled at 22 kHz, where only every second audio sample is used.The digital signal produced after such under-sampling results inaliasing that shifts and inverts the frequency spectrum so that itappears in the 2 kHz to 4 kHz range. A zero crossings detector 86 thenidentifies where the audio signal changes sign. The zero crossing pointis then more accurately calculated in the frequency estimation step 88by linearly interpolating between samples either side of the zerocrossing. In this example, a frequency estimate is only required every3.33 ms, for it demodulated output signal at 300 Hz. This is achieved bycounting the number of zero crossings and measuring the period over thenearest fixed number of cycles during this period, providing a fixed 300Hz output. The demodulated output is then inverted to correct for thefrequency spectrum being inverted by the under-sampling operation.Finally the 300 Hz demodulated ECG data is passed through a 40 Hz lowpass filter since the ECG bandwidth of interest is below 40 Hz. Thisfurther reduces any noise from the frequency estimates and demodulatedoutput. The FM demodulator outputs 16 bit, 300 Hz ECG.

Sensor input 74 can also include real-time information from additionalsensors as well as user input 74′. For example, in embodiments whereinthe computing device 16 is a smartphone 30, the input 74 can includereal-time information from a GPS and/or accelerometer in the smartphone30 in addition to the demodulated digital ECG data. User input 74′ canalso include spoken voice messages entered through a microphone of thecomputing device 16. Instructions 72 can cause the sensor and/or userinput 74 and 74′ to be recorded and maintained in a storage memory 56 ofthe computing device 16.

In one embodiment, the set of instructions 72, when executed by the oneor more computing devices 16, can further cause the one or morecomputing devices 16 to calculate and display in real-time, a heart raterepresented by the frequency modulated ECG ultrasonic signal. Inaddition, demodulated digital ECG data can be processed to identify theoccurrence of an arrhythmia. In such designs, the storage medium 70 caninclude instructions 72 to cause the computing device 16 to display awarning on a display screen 58 or emit an audible alert through thespeaker 76 at the occurrence of an arrhythmia.

Instructions 72 can cause the computing device 16 to store thedemodulated digital ECG data in a memory 56 of the one or more computingdevices 16 for later retrieval. The set of instructions 72 can furthercause the one or more computing devices 16 to retrieve and transmit,upon demand, the stored demodulated digital ECG data to a web server 52via an internet connection on the computing device 16. Recorded spokenvoice messages can be stored and transmitted to the web server 52,simultaneously with the demodulated digital ECG data.

In other embodiments, the instructions 72 can cause the one or morecomputing devices 16 to transmit the demodulated digital ECG data,and/or voice messages, to the web server 52 in real-time.

A version of the smartphone software is packaged as a software librarythat can be integrated with other third party software applications.This provides a simplified and standard method for third partyapplications to use the ECG device 10′ to obtain heart rate and otherderived information without having to develop their own dataacquisition, demodulation, and signal processing algorithms.

A version of the software also runs on a PC and includes demodulation,processing, storage and transmission to the web server 52. The softwareincludes the audio acquisition, demodulation, ECG analysis, andacceleration analysis modules.

Audio samples from the ADC are optionally passed through a digitalband-pass filter to remove unwanted frequencies outside the modulationrange. The demodulation module demodulates the frequency modulated ECGultrasonic signal using undersampling at about one-half the frequency ofthe audio sample to shift the spectrum to a lower frequency range,followed by a linear approximation and zero crossings algorithm. Thedemodulator allows selection of different modulation parameters to matchthe particular ECG device. While demodulation using zero crossings andlinear approximation alone works well for carrier frequencies 6 kHz andlower, above 10 kHz with 44 kHz sampling, the errors from linearapproximation become large unless undersampling is used to shift thespectrum.

The algorithm then looks at the sign of incoming data. When the signchanges it draws a straight line between the two points and interpolatesthe zero value. It uses this to determine the average frequency over a3.333 ms interval, which provides ECG data at the output sampling rateof 300 Hz.

The ECG analysis module includes algorithms that process the ECG todetect and classify beats, and provides a heart rate estimate.Beat-to-beat heart rate is calculated from the interval between heatsand a more robust measurement of heart rate is calculated using medianfiltering of the RR intervals.

The acceleration analysis module includes algorithms that processsignals from the built-in 3 axis accelerometer sensor in the smartphone30, to derive an estimate of a person's energy expenditure, steps,cadence, and body position and to detect falls.

From the above descriptions, it is clear that the presently disclosedand claimed inventive concept(s) are well-adapted to carry out theobjects and to attain the advantages mentioned herein, as well as thoseinherent in the presently disclosed and claimed inventive concept(s).While the presented embodiments have been described for purposes of thisdisclosure, it will be understood that numerous changes may be madewhich will readily suggest themselves to those skilled in the art andwhich are accomplished within the spirit of the presently disclosed andclaimed inventive concept(s).

What is claimed is:
 1. A mobile ECG sensor comprising: an electrodeassembly comprising electrodes, wherein the electrode assembly sensesheart-related signals when in contact with a user's skin, and produceselectrical signals representing the sensed heart-related signals; aconverter assembly electrically connected to the electrode assembly,configured to convert the electrical signals to a modulated signal,wherein the modulated signal carries the electrical signals representingthe sensed heart-related signals; a transmitter that transmits themodulated signal wirelessly to a computing device; and a housingcontaining the electrode assembly, the converter assembly, and thetransmitter, wherein the housing is a credit card form factor.
 2. Themobile ECG sensor according to claim 1, wherein the electrode assemblycomprises at least two electrode pads positioned on an exterior surfaceof the credit card form factor.
 3. The mobile ECG sensor according toclaim 2, wherein the credit card form factor comprises a top part with atop surface and an underside, and a bottom part with a topside and abottom surface, wherein the underside of the top part is affixed to thetopside of the bottom part, wherein the electrode assembly furthercomprises at least two conductive flexible membranes electricallyconnected to the at least two electrode pads and electrically connectedto the converter assembly, and wherein the at least two electrode padsare positioned on the top surface of the top part, and the at least twoconductive flexible membranes are positioned between the underside ofthe top part and the topside of the bottom part.
 4. The mobile ECGsensor according to claim 2, wherein the at least two conductiveflexible membranes are in contact with the at least two electrode pads.5. The mobile ECG sensor according to claim 1, wherein the modulatedsignal is a frequency modulated signal, and wherein the transmitteroutputs the frequency modulated signal having a carrier frequency in arange of from about 6 kHz to about 20 kHz.
 6. The mobile ECG sensoraccording to claim 1, wherein the modulated signal is in accordance witha Bluetooth wireless communication standard.
 7. The mobile ECG sensoraccording to claim 1, wherein the modulated signal is in accordance witha headset profile of the Bluetooth wireless communication standard.
 8. Amobile ECG sensor comprising: a credit card form factor, wherein thecredit card form factor houses: an electrode assembly comprisingelectrodes positioned on an exterior surface of the credit card formfactor, wherein the electrode assembly senses heart-related signals whenin contact with a user's skin, and produces electrical signalsrepresenting the sensed heart-related signals; a converter assemblyelectrically connected to the electrode assembly, the converter assemblycomprising a processor; a display electrically connected to theconverter assembly, the display positioned on the exterior surface ofthe credit card form factor; and a memory comprising instructions tocause the processor to process the sensed heart-related signals anddisplay the heart-related signals on the display.
 9. The mobile ECGsensor according to claim 8, wherein the heart-related signals compriseECG signals.
 10. The mobile ECG sensor according to claim 8, wherein theheart-related signals comprise heart rate signals.
 11. The mobile ECGsensor according to claim 8, further comprising a transmitterelectrically connected to the processor and housed in the credit cardform factor, wherein the transmitter is capable of transmitting theprocessed sensed heart-related signal wirelessly.
 12. A mobile ECGsensor comprising: an electrode assembly comprising electrodes, whereinthe electrode assembly senses heart-related signals when in contact witha user's skin, and produces electrical signals representing the sensedheart-related signals; a converter assembly electrically connected tothe electrode assembly, configured to convert the electrical signals toa modulated signal, wherein the modulated signal carries the electricalsignals representing the sensed heart-related signals; a transmitterthat transmits the modulated signal wirelessly to a computing device;and a housing containing the electrode assembly, the converter assembly,and the transmitter, wherein the housing is a mobile phone case formfactor, and wherein the electrodes are positioned on an exterior surfaceof the mobile phone case form factor.
 13. The mobile ECG sensoraccording to claim 12, wherein the modulated signal is a frequencymodulated signal, and wherein the transmitter outputs the frequencymodulated signal having a carrier frequency in the range of from about 6kHz to about 20 kHz.
 14. The mobile ECG sensor according to claim 12,wherein the modulated signal is in accordance with a Bluetooth wirelesscommunication standard.
 15. The mobile ECG sensor according to claim 12,wherein the modulated signal is in accordance with a headset profile ofthe Bluetooth wireless communication standard.